The designation of the protection areas of the Main Groundwater Reservoirs for the purposes of planning and water management in the river basins requires identifying areas that threaten the quality of the groundwater. Essential conditions for groundwater management include the assessment of the possibility of the migration of pollutants in the filtration stream and the definition of factors ensuring a balance between the pollutants accumulated in the solid phase of the soil and groundwater. The risk of launching the accumulated pollutants in the solid phase of the soil may be caused by both the changes of the pressure gradients in the aquifers and the hydrogeochemical balances in the examined system.
The results of the authors’ research and the literature on the subject (Małecki 1998, Wildi et al. 2004, Gruszczyński, Małecki 2010, Małecki et al. 2017, Postma et al. 2017, Małecki, Ziułkiewicz 2019) indicate that such threats occur in river valley zones, which have been the places of discharge of sewage from large urban agglomerations for decades. It is necessary to recognise the geological structure and the hydrogeological conditions, with particular emphasis on the assessment of the occurrence of aquifers and aquitards, including their nature and hydrogeological features. The hydraulic relationships between the surface water and groundwater and the relationships between aquifers are basic elements determining the sensitivity of the hydrogeological system to pollution, especially in river valley zones exposed to strong anthropopressure (Wu et al. 2007). This type of assessment requires extended (dedicated) hydrogeological and hydrogeochemical studies. The current paper focuses on the scope of the research assessing the pollution risk of the aquifer, namely, the aquifer of the Upper Cretaceous. According to the authors, a good testing field for this type of assessment is the Ner river valley, located near the large urban agglomeration of Łódź (central Poland) within the limits of the Main Groundwater Reservoirs No. 401 – Łódź basin.
The Ner is a right tributary of the Warta River, flowing from the Łódź Hills through the Laska Upland and the Kolska Valley, flowing out at an altitude of about 208 m a.s.l. to the south-east from Łódź (Penczak et al. 2010). The average width of the river bed in its upper course is 12 m with the width of the valley from 300 m to 900 m (Fig. 1). The average annual flow of the Ner in the lower course (Dąbie section) according to (IMGW 2023) for the period 2010–2021 is 8.0 m3 · s−1.
Documentation map of the research area.
In the upper part of the Ner River near Konstantynów Łódzki, a sewage treatment plant has been operating since 1930. For decades, heavily polluted wastewater from the industrial agglomeration of Łódź (textile industry and related dyeing plants) has been discharged. This wastewater, which is only mechanically treated, has deteriorated the water quality of the Ner River and also that of the Warta River that flows at the estuary of the Ner River. This wastewater has also caused the accumulation of pollutants in the alluvial valley formations (Lis, Pasieczna 1998). Wastewater has been subjected to more effective treatment, including biological treatment, since 1997. Currently, the Group Wastewater Treatment Plant in Konstantynów Łódzki treats 51% of all the wastewater from the Łódź Voivodeship, which is approximately 210,000 m3 · day−1 on average (ZWiK 2022). Using the slope of the terrain, the sewage system gravitationally transports municipal sewage from the Łódź agglomeration, including storm sewage, from the city towards the Ner river basin. In addition, during periods of torrential rains, accumulated pollutants in the form of suspensions are washed off the city surface. This leads to an increase in pollutant loads in the mixture of household and precipitation sewage. This unfavourable phenomenon is intensified by the combined sewage system in the downtown part of the city.
For decades, rainwater from the city was also used to irrigate the grasslands of the Ner valley. Irrigation resulted in the accumulation of pollutants in the soil profile of meadow complexes, which potentially threaten the quality of groundwater of the Quaternary (Q) and the Upper Cretaceous (Cr3) aquifers within the boundaries of the Main Groundwater Reservoir No. 401 – Łódź Basin.
The study area is located in the Ner river valley in the western foreground of the Łódź Hills, in the mesoregion of the Łaska Upland, belonging to the macroregion of the South Wielkopolska Lowland (Solon et al. 2018). The Upper Ner Valley is located within the large geological structure of the Mogilno – Łódź Basin, on the eastern side of the Lutomiersk Anticline near Konstantynów Łódzki, which belongs to the Łódź agglomeration. Both peripheries of this anticline are strongly dislocated. In the Mesozoic formations, height differences reaching 600–700 m are noticeable (Baliński 1992, Ziułkiewicz 2003). The Lutomiersk Anticline marks the western border of the Main Groundwater Reservoir No. 401, created to protect groundwater resources in the limestone formations of the Łódź Basin.
In the area of Konstantynów Łódzki, the main usable aquifer is the Upper Cretaceous, composed of varied limestone and marls. Numerous tectonic structures and lithological diversity of the Upper Cretaceous aquifer result in significant diversification of its hydrogeological parameters, as indicated by the values of its transmissivity, from below 100 m2 · day−1 to over 1000 m2 · day−1 (Fabianowski 2002).
The Cenozoic formations of the moraine plateau, within which the test site is located, are dominated by Quaternary glacial tills with local interbeddings of sands and gravels. Conditions for the occurrence of groundwater in the Cenozoic formations can be considered good only in the river valley where erosion reached to the ceiling of the Mesozoic formations (Fig. 2). Water reservoir conditions are created there in thicker clastic formations. The contemporary bottom of the Ner valley is built of deposits from the Late Vistulian and Holocene. These are various-grained and fine-grained sands of river origin, sometimes underlain by fluvioglacial sands and, to a lesser extent, hardly permeable stagnant formations (Balwierz, Piwowarski 2008, Kittel 2012, Brzeziński, Gałązka 2013). Within the valley, there is one Quaternary aquifer present in the alluvial formations drained by the river.
Hydrogeological cross-section (line of cross-sections shown in Fig. 1).
The range of the Neogene aquifer is very limited. It occurs within the local depressions of the Upper Cretaceous top or the forms of glacitectonic ‘extrusion’ (Bierkowska et al. 1990).
The Ner river valley is a regional drainage base for Cenozoic and Upper Cretaceous aquifers. The lateral inflow of groundwater is mainly from the south, as it is limited from the northeast by the watershed between the Warta and the Vistula. The watershed in the upper part of the Ner catchment is also the western border of the Upper Cretaceous regional depression cone of the Łódź agglomeration. The development of the depression cone in the Quaternary formations began to move towards the Ner river valley, covering the north-eastern part of the city of Konstantynów Łódzki (Fig. 3).
The extent of the depression cone in the Quaternary aquifers of the Łódź agglomeration as a part of Main Groundwater Reservoir No. 401 (Rodzoch et al. 2013).
The analysis of the head contours of the Upper Cretaceous and Quaternary aquifers shows their hydraulic connection in zones where there are no impermeable formations (Fig. 4).
Groundwater table of the Quaternary and Upper Cretaceous aquifers in the area of modelling studies.
In the 1980s, work was carried out on the design construction of the ‘Lutomiersk’ purified water reservoir in the Ner river valley. The main objective of the archival research was to determine the impact of the reservoir water on the groundwater of the usable Cretaceous aquifer. This impact was assessed on the basis of hydraulic relationships between surface water and groundwater and relationships between the Quaternary and Cretaceous aquifers, with the indication of zones of possible leakage from the Quaternary into the Upper Cretaceous. When assessing the threat to usable aquifers in the Ner river valley today, the above-mentioned archival research results were taken into account, especially the research of the hydrodynamic balance changes in the Upper Cretaceous formations (Murzynowski, Małecki 1982).
As part of the mentioned work in the Ner river valley, C, E and H pumping wells with observation wells were tested (Fig. 1). The E well is located in the zone of full contact between the Quaternary aquifer and the Cretaceous aquifer (Fig. 2). The C well is located in an area where the contact between the Quaternary and the Cretaceous aquifers could be limited by a layer of weathering, about half a meter thick, and the H well is in the zone with the contact between the Neogene and Cretaceous aquifers limited by a two-meter layer of limestone weathering. The contact between the subsurface Quaternary aquifer and the Neogene aquifer is strongly limited by 25–30 m thick Pliocene clays and silts (Fig. 5).
Hydrogeological cross-sections (lines of cross-sections shown in Fig. 1, explanations to cross-sections shown in Fig. 2).
In the C well, a stabilised self-outflow was obtained at the level of 1.5 m a.g.l., which corresponds to 157.0 m a.s.l, and in piezometers, the water table in Quaternary sands and gravels was 0.9 m b.g.l., which corresponds to 154.6 m a.s.l. In the C location, piezometric pressure differences between Cr3 and Q amounted to about 2.4 m. No aquitards between the Cretaceous and Quaternary aquifers were found in the E location. The unconfined head stabilised at a depth of 0.86 m b.g.l., and the pressures in the Cretaceous and Quaternary aquifers were at the same level. In the H location, below a series of Quaternary formations, significant thicknesses of the Neogene clay formation with brown coal inserts and clayey weathered limestone were found; these formations constituted the aquitards above the Cretaceous aquifer. In the H well, self-outflow was obtained, stabilising at about 4 m a.g.l., which corresponds to 162 m a.s.l. The unconfined Quaternary groundwater table in the piezometers was at a depth of 0.9 m b.g.l. The pressure difference between Cr3 and Q in this location was 4.9 m (Table 1).
Basic information about C, E and H pumping wells and observation wells.
Pumping and observation wells | Well name | Well depth | Aquifer stratigraphy | Aquifer lithology | Piezometric water table | Water table |
---|---|---|---|---|---|---|
[m] | [m b.g.l.] | |||||
C | C pumping well | 30 | Cr3 | limestones | −1.50 | 13.50 |
P-1 observation well | nd | Q | nd | 0.59 | 0.59 | |
1 observation well | 14 | Q | sands and gravels | 0.90 | 0.90 | |
P-2 observation well | nd | Q | nd | 0.95 | 0.95 | |
E | E pumping well | 35 | Cr3 | limestones | 0.86 | 0.86 |
P-5 observation well | 17 | Q | sands of different granulation | 1.46 | 1.46 | |
P-6 observation well | 18 | Q | sands of different granulation | 0.91 | 0.91 | |
P-7 observation well | 18 | Q | sands of different granulation | 2.30 | 2.30 | |
H | H pumping well | 70 | Cr3 | limestones | −4.00 | 53.50 |
P-10 observation well | 22 | Q | sands and gravels | 0.40 | 0.40 | |
P-11 observation well | 12 | Q | sands and gravels | 1.00 | 1.00 | |
P-15 observation well | 18 | Q | sands and gravels | 1.80 | 1.80 |
nd – no data.
To confirm the existence of contact zones between the Upper Cretaceous and Quaternary aquifers, the hydrodynamic balance in the Cretaceous formations in the C, E and H locations was disturbed, which was only possible when the maximum discharge rate of the well was exceeded (Murzynowski, Małecki 1982). In the H location, during pumping, no correlation was found between the lowered pressure of the Cretaceous groundwater table and the Quaternary groundwater table level. A different dependence was found in the E location. Observation piezometers showed a straight reaction to changes confirmed in the depression in both aquifers. The analysis of pressures indicates that in this zone, there is leakage of the Cretaceous aquifer to the Quaternary aquifer. The C location showed less interdependence between the Cretaceous and Quaternary groundwater tables during pumping (Fig. 6).
Observations of the groundwater table level during pumping in the C, E and H wells.
Changes in the hydrodynamic balance of the Cretaceous aquifer have shown that despite the existence of significant pressure values in the Cretaceous (well H – 39.22 kPa, the C well – 14.71 kPa), there are zones (the E well) where pressure reduction in the Upper Cretaceous aquifer will be led to the drainage of Quaternary groundwater and the occurrence of potential hazards to the chemical status of groundwater of the Cretaceous aquifer.
The pumping of the E, H and C wells also allowed determining the filtration parameters of the Cretaceous complex. Calculations of the conductivity were made in accordance with the methodology provided in the guidebook by Dąbrowski and Przybyłek (2005) (Table 2).
Results of calculations of the filtration parameters of the Upper Cretaceous aquifer based on pumping of the H, C and E wells.
Well | Pumping type | Pumping stage | Discharge rate Q | Stabilized depression s | Conductivity k | Average conductivity k | Depression cone radius during pumping test | Permissible discharge rate Q max |
---|---|---|---|---|---|---|---|---|
[m3 · h−1] | [m] | [m · s−1] | [m · s−1] | [m] | [m3 · h−1] | |||
H | one stage | 1 | 39.5 | 35.73 | 1.19 · 10−5 | 370.1 | 7 | |
C | one stage | 1 | 100.0 | 5.63 | 3.58 · 10−4 | 320.0 | 41 | |
E | three stages | 1 | 24.7 | 6.80 | 8.16 · 10−5 | 5.53 · 10−5 | 168.0 | 11 |
2 | 40.4 | 14.90 | 5.05 · 10−5 | 376.0 | ||||
3 | 51.6 | 24.30 | 3.37 · 10−5 | 612.0 |
The obtained values of the conductivities were helpful in creating a hydrodynamic groundwater model enabling the assessment of the relationship between the water of the Quaternary and Cretaceous aquifers.
Model tests were carried out in the Visual ModFlow Flex 7.0, Waterloo Hydrogeologic program, based on an algorithm using the finite difference method (McDonald, Harbaugh 1988). The model was made for the steady-state conditions, defined as the average annual hydrodynamic state representing the period of 1976–2021. The aim of the modelling studies was to determine the possibility of infiltration of surface water in the Ner river valley and leakage of Quaternary aquifer groundwater as a result of the decrease in piezometric pressures in the Upper Cretaceous aquifers caused by water withdrawal in Ignacew, by the Municipal Company of Konstantynów Łódzki Spółka z o.o.
The conceptual model was based on the separation of a fragment of the aquifer system of the Konstantynów Łódzki region, with the assumption that with such a large area there would be no direct impact of the boundary conditions on the area of water inflow to the Ignacew wells. The conceptual model was constructed based on the recognition of the hydrogeological conditions of the area. Water circulation in this hydrogeological system occurs in the Quaternary, locally Neogene aquifer and main usable aquifer in the Upper Cretaceous formations.
The model included an area of 71.85 km2 within the range of occurrence of hydrogeological units 1Q/baCr3II and 2bCr3II according to the Hydrogeological Map of Poland, scale 1:50,000, Łódź Zachód sheet (Fabianowski 2002). The side boundaries were drawn as follows:
– northern border: along the course of the Lubczyna River, – western border: along the course of the Zalewka River, then along the course of the Ner River, – southern border: along the head contour of 170 m a.s.l. in the Upper Cretaceous aquifer (Rodzoch et al. 2013), and – eastern border: along the head contour of 180 m a.s.l. in the Quaternary aquifer (Rodzoch et al. 2013).
The upper surface of the model research object is the groundwater table of the subsurface aquifer occurring in the Quaternary formations. For most of the area, it remains unconfined. The bottom model surface was assumed as the bottom of the Upper Cretaceous formations. This surface is characterised by small denivelations of 360 m from -152 m a.s.l. to -410 m a.s.l., which corresponds to depths from 312 m b.g.l. to 589 m b.g.l. It is inclined towards the south-east.
Exchange of water with the environment of the system takes place as a result of:
– infiltration and evaporation from the surface of the shallow groundwater occurrence, in the river valleys; – groundwater inflow from the south and east outside the mapped system (lateral inflow to aquifers); – direct drainage through larger rivers: Ner, Lubczyna, Zalewka and their tributaries, including drainage ditches; indirect drainage in river valleys through erosive hydrogeological windows; and – lateral outflow of groundwater to the northwest, according to the Fabianowski (2002).
The area was divided into square cells of size x = 50 m, y = 50 m, 175 rows and 304 columns; the number of active cells was 28,740.
The discretisation of the area in the vertical direction covered the distinction of seven layers described in order from the top:
– first: subsurface aquifer (Q1), – second: glacial tills constituting an aquitard , locally discontinuous in river valleys (Q1–Q2), – third: Quaternary usable aquifer, according to the record of the hydrogeological unit, locally the Neogene aquifer (Q2 –Ng), – fourth: glacial tills or silts and clays constituting an aquitard , locally discontinuous in river valleys (Q2–Ng–Cr), – fifth: top part of the Upper Cretaceous aquifer, at a depth of 12 m in the Ner valley to 91 m in the eastern part of the area (marked as Cr3−1), – sixth: the middle part of the Upper Cretaceous aquifer, characterised by weaker filtration parameters due to the smaller share of fracturing, at a depth of 62 m in the Ner valley to 143 m (marked as Cr3−2), and – seventh: the lower part of the Upper Cretaceous aquifer, characterised by the weakest filtration parameters, at a depth of 228 m in the north to 313 m in the south-eastern part (marked as Cr3−3).
The thicknesses of the individual layers were determined on the basis of the borehole profile cards, in accordance with the Central Hydrogeological Data Bank (CBDH). For the model, it was assumed that the minimum thickness of the layer is 5 m to maintain the stability of the calculations in places where the aquitards were discontinuous.
Research work in the Ner river bed was carried out in October 2022, in three profiles (H, E and C), at a distance of approximately 5 km below the point of discharge of sewage from the Group Sewage Treatment Plant, on the day when 1.71 m3 · s−1 of post-treatment water was discharged into the river, i.e. slightly below average for October 2022 (1.83 m3 · s−1). Approximately 1.69 m3 · s−1 of water flowed down the river bed, which almost corresponded to the amount of water discharged from the Group Sewage Treatment Plant.
Samples of river sediments in the E, C and H profiles were collected from the river bed using a sludge pipe. Sampling sites were selected on the basis of earlier gradientmeter measurements of water flow directions in river alluvium. Places representing zones of river water infiltration into the bottom of the channel, as well as places of its drainage after mixing with groundwater, were selected (Fig. 1). Determination of chemical elements in river sediments was carried out using the aqua regia extraction method. The content of elements in the obtained filtrate was determined by the ISO 11885/ISO 17294-2 method in the Wessling laboratory and by ICP-OES emission spectrometry using a Perkin-Elmer device in the Laboratory of Geomicrobiology and Environmental Geochemistry of the Faculty of Geology, University of Warsaw.
Cation exchange capacity (CEC) was also determined in the sediments collected from the Ner river bed. The CEC value was estimated by the Breeuwsma formula (Appelo, Postma 1993), based on the percentage of particles <2 m and the percentage of organic matter. The percentage content of particles <2 m was determined based on the analysis of the granulometric composition of the samples, while the content of organic matter was determined using the loss on ignition method. In addition, in all samples, the CEC was determined by the Kappen method. The research was carried out in the Applied Geology Laboratory of the Faculty of Geology, University of Warsaw.
Groundwater samples from the Quaternary, Neogene and Cretaceous aquifers were collected directly from the wells. Water samples in the alluvium were collected from the Ner river bed, 20 cm below the bottom of the river, using a gradientmeter, and river water samples were taken directly from the main stream (Hr and Er points). The location of the documentation points is marked in Figure 1.
In each of the water samples in the field, the following measurements were made: water temperature, pH and electrolytic conductivity with a multifunctional Eijkelkamp device. Measurements of the red-ox potential and the content of dissolved oxygen were performed with a multifunctional device CX-401 by Elmetron. Samples for chemical analysis were collected in bottles made of HDPE plastic, which is inert towards water. Whatman filters of 0.45 m were used for sample filtration. Samples for testing by emission spectrometry were fixed directly in the field with concentrated 65% pure nitric acid. The analyses were carried out in accordance with the recommendations of Witczak et al. (2013). Anion content was determined by the colorimetric or spectrophotometric method in the Applied Geology Laboratory of the Faculty of Geology, University of Warsaw, while Ag, Al, As, Ba, Be, Bi, Br, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, Ni, Pb, Si, Sn, Sr, Ti, V, W and Zn by the ISO 11885/ISO 17294-2 method in the Wessling laboratory and by ICP-OES emission spectrometry with a Perkin-Elmer device in the Geomicrobiology and Geochemistry Laboratory Environment at the Faculty of Geology of the University of Warsaw.
To more fully characterise the chemistry of the tested water, models of the solution state were made. The models were made in the Geochemist’s Workbench (2023) program with the thermo.tdat thermodynamic database, supplemented with forms of bismuth and cadmium. The selected thermodynamic database allows for the full range of water components to be included in the calculations. If the contents of individual components were lower than the limit of their detection (DL), half of the DL was adopted for model calculations.
The conductivities of the individual layers were subject to changes at the calibration stage. The initial values were adopted on the basis of own calculations from test pumpings, data from borehole charts (CBDH) and result maps of the modelled Main Groundwater Reservoir No. 401 on a regional scale (Rodzoch et al. 2013). The isotropy of the medium in the directions (
The values of infiltration recharge were mapped using the II type boundary condition (
In the study area, the groundwater withdrawal was mapped as a type II point condition with known outflow rate, adopted on the basis of data obtained from the POBORY database, Polish Geological Institute-National Research Institute (average value over many years).
The III type boundary condition represented drainage through watercourses and the lateral inflow through the model boundaries (Fig. 7). The III type RIVER condition was set for model cells simulating rivers characterised both as boundaries of the model and within the model. For this condition, the width of the watercourses was introduced, the layer of water in the watercourses was adopted on the basis of field observations, supplemented with data from the Map of the Hydrographic Division of Poland in the scale of 1:200,000 (Czarnecka 2006). The DRAIN condition was set at the drainage ditch courses visible in the image of the WMS orthophotomap service (GUGiK 2023).
Model structure and boundary conditions: RIVER (blue), WELL (brown), DRAIN (purple), general head boundary (green), 3D view from the south, exaggeration of the vertical scale · 10.
The condition of the III type – General Head Boundary (GHB) – was used to map the vertical boundaries of the model along a separate fragment of the system. After the hydrogeological analysis, it was found that the boundaries of the modelled system are open to water exchange with the surroundings from the south and east for the first layer and from all sides for deeper layers.
The calibration process consisted in finding a solution to the inverse problem by the method of successive approximations. The solution found for the condition of the aquifer system was confirmed by calibrating the heads at 180 points, including aquifers marked as Q1, Q2– Ng, Cr3_1 and Cr3_2. In the calibration process, the properties of the filtration field were refined by increasing or decreasing the conductivity. The obtained range of values was slightly lower than the initial values: from 0.8 m · day−1 to 5 m · day−1 for the subsurface aquifer (model layer no. 1) and 5–10 m · day−1 for the Quaternary aquifer (model layer no. 3). The conductivity of the top part of the Upper Cretaceous was determined at 4–7 m · day−1, the middle part at 3 m · day−1 and the bottom part at 1 m · day−1. The conductivity of aquitard formations was set to the value of water permeability in the range of 0.00005–0.05 m · day−1.
As a result of the calibration, errors characterising the compliance of the model calculation results with the input data at the calibration points were determined (Fig. 8). The maximum difference between the measured and calculated heads was -11 m; the absolute mean was 2.81 m. The estimation error of 0.27 m and the absolute mean error of 3.68 m were considered low enough to complete the calibration process and to recognise the credibility of the obtained model. During the calibration, special attention was paid to adjusting the modelling results to the groundwater levels at the Ignacew wells, assuming the position of the dynamic water table caused by the withdrawal (concordance approx. 1 m).
Model calibration chart.
The Ignacew wells’ (A1, A2, A3) work was mapped by assigning appropriate discharge rate. During field works, it was found that the actual value of withdrawal is similar to the value approved in the water law permit and amounts to approximately 90% (Table 3). To assess the impact on the Quaternary aquifer and the surface water of the Ner River, remaining in hydraulic contact with the Upper Cretaceous aquifer, the heads of all aquifers were determined in quasi-natural conditions with inactive wells’ simulation and in the conditions of the active wells.
Discharge rate and the depression size for the Ignacew-intake wells.
Well no./ No. According to the Central Hydrogeological Database | Aquifer and its screened part | Exploitable / actual discharge rate | Depression size |
---|---|---|---|
[m3 · d−1] | [m] | ||
A1 / 6270670 | Cr3−1 (upper part) | 3871.2 / 3360.0 | 20.1 |
A2 / 6270689 | Cr3−1, Cr3−2 (upper and central part) | 3508.8 / 3120.0 | 21.4 |
A3 / 6270681 | Cr3−1, Cr3−2 (upper and central part) | 2805.6 / 2520.0 | 20.7 |
The numerical model of the filtration field made it possible to determine the 25-year time (
Model tests have shown that when pumping the Ignacew well with the assumed actual rate, the water inflow comes from different directions: for the A1 well, from the north and south ; for the A2 well, from the east and south and for the A3 well, from the south and south-east (Fig. 9). The inflow to all wells is through the Ner river valley in the area of C and E research profiles and hydrogeological sections, where the presence of hydrogeological windows between the Quaternary and Cretaceous aquifers was found. The range of influence of the well on the river valley is the smallest for the A2 well and the largest for the A3 well. The inflow time ranges from 1 year to 25 years, and at the intersection with the Ner river bed, it is from 6 years to 15 years. The work of A1, A2 and A3 wells with assumed rate causes a local reversal of piezometric pressures (Fig. 10). In the Ner valley, the Upper Cretaceous aquifer groundwater table is lower than the Quaternary aquifer, which makes it possible for surface water to infiltrate to the main usable aquifer. This depression ranges from 0.04 m to 1.99 m (the largest on the northern border of the valley), while in natural conditions, the level of the Upper Cretaceous table was higher than the Quaternary with a value of 0.01–0.39 m.
Layout of the stream line on the way of water inflow to the Ignacew-intake wells as a result of model research.
Head difference between the Quaternary and the Upper Cretaceous aquifers as a result of flow modelling in conditions of: A – average head without withdrawal; B – average head with actual withdrawal from the POBORY database.
Since the previous studies, including model studies, showed the possibility of seepage of water from the vadose zone and leakage of water from the overlying layers to the Upper Cretaceous aquifer, the next stage of work was to determine the potential migration risk of pollutants accumulated in the overlying layers. For this purpose, sorption parameters of river sediments, accumulated pollutants in them and the chemical composition of surface water and groundwater were determined.
The results of laboratory analyses of the element content in the collected samples of the Ner alluvium (Table 4) were compared with the archival data contained in the Hydrogeochemical Atlas of the Łódź agglomeration (Lis, Pasieczna 1998). The contents of most elements in the alluvium are small and definitely lower than the average values determined for the entire agglomeration area. The exceptions are cadmium, chromium, copper, mercury, strontium, silver and zinc. Chromium content higher than average was found in all tested samples. According to Lis and Pasieczna (1998), the main potential source point of contamination with this element are discharges of sewage into the tributaries of the Ner, i.e. the Łódka and Dobrzynka rivers. The estuary of the Łódka is located 1.8 km from the farthest upstream Ner, the H cross-section (Fig. 5). In 1998, the Łódka alluvial had the highest average chromium content in the entire area of the agglomeration, amounting to 102 ppm. The highest content of chromium in a single measurement (977 ppm) was determined in the Dobrzynka alluvium, whose estuary to the Ner is located from the H-section at a distance of about 6 km upstream. In the tested samples, the highest concentrations of chromium were found in the H-section (69.60 ppm at H2). The decrease in the content of this element in individual research profiles follows the direction of the flow of the Ner, up to the value of 18.7 ppm at point C2 located in the most downstream C section (Table 4).
Contents of elements in the sediments of the Ner River (values greater than the average are marked in red)*.
Concentration | Sampling site | Łódź Agglomeration | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Element | Unit | H1 | H2 | H3 | E1 | E2 | E3 | C1 | C2 | C3 | max–min (average)** |
Ag | ppm | 0.38 | 1.77 | 0.76 | 0.48 | 0.62 | 0.28 | nd | nd | nd | <1–198 (<1) |
Al | % | 0.02 | 0.06 | 0.01 | 0.02 | 0.02 | 0.01 | 0.01 | 0.01 | 0.01 | <0.01–3.74 (0.21) |
As | ppm | 0.66 | 2.16 | 1.84 | 0.77 | 1.06 | 0.61 | <0.1 | <0.1 | <0.1 | <5–906 (<5) |
Ba | ppm | 10.08 | 40.2 | 8.02 | 12.96 | 12.44 | 5.98 | 5.92 | 7.95 | 7.27 | 3–484 (42) |
Bi | ppm | 200 | 640 | 76 | 280 | 300 | 66 | 0.1 | <0.1 | 0.07 | nd |
Pb | ppm | 9.6 | 40 | 5.68 | 11.4 | 13.26 | 4.72 | 2.93 | 2.12 | 3.88 | <5–10 200 (15) |
Br | ppm | 56 | 58 | 54 | 66 | 44 | 66 | <0.1 | <0.1 | <0.1 | nd |
Cd | ppm | 1.45 | 1.09 | 0.64 | 0.69 | 1.14 | 1.19 | 0.3 | 0.27 | 0.42 | <0.5–59.6 (0.6) |
Ca | % | 0.1 | 0.61 | 0.05 | 0.1 | 0.1 | 0.06 | 0.04 | 0.04 | 0.04 | 0.02–16.90 (0.42) |
Cr | ppm | 27.6 | 69.6 | 47.4 | 32 | 42.8 | 36 | 19.56 | 18.7 | 20.2 | <1–977 (5) |
Co | ppm | 0.66 | 0.68 | 0.46 | 0.66 | 0.72 | 0.37 | 0.45 | 0.29 | 0.27 | <1–46 (2) |
Fe | % | 0.08 | 0.22 | 0.09 | 0.06 | 0.08 | 0.06 | 0.03 | 0.07 | 0.03 | 0.03–11.80 (0.45) |
K | ppm | 29 | 32.4 | 23 | 33.2 | 28.8 | 18.84 | 12.51 | 9.91 | 12.3 | nd |
Cu | ppm | 10.42 | 38.6 | 11.12 | 14.58 | 18.68 | 8.66 | 5.69 | 4.62 | 6.85 | <1–1720 (9) |
Mg | % | 0.01 | 0.02 | <0.01 | 0.01 | 0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01–0.92 (0.06) |
Mn | ppm | 23.2 | 40.8 | 4.84 | 11.02 | 7.2 | 6.58 | 4.73 | 69.64 | 5.58 | 4–2 896 (129) |
Mo | ppm | <0.1 | 0.12 | 0.3 | 0.3 | 0.23 | 0.12 | 0.03 | <0.1 | 0 | nd |
Na | ppm | 33.4 | 48.4 | 33.6 | 62.2 | 36.2 | 26.2 | 16.13 | 16.99 | 13.29 | nd |
Ni | ppm | 1.4 | 2.5 | 1.83 | 1.63 | 2.06 | 0.68 | 0.96 | 0.6 | 0.55 | <1–345 (4) |
Hg | ppm | 0.25 | 0.74 | 0.39 | 0.4 | 0.45 | 0.26 | nd | nd | nd | <0.05–20.50 (0.06) |
Sr | ppm | 2.92 | 14.78 | 3.84 | 2.9 | 2.72 | 1.36 | 1.29 | 2.78 | 1.58 | <1–269 (13) |
Ti | ppm | 6.56 | 13.18 | 3.36 | 6.26 | 6.98 | 3 | 1.88 | 1.3 | 2.67 | 4–528 (30) |
V | ppm | 0.9 | 2.24 | 0.9 | 0.95 | 1.07 | 0.75 | 0.32 | 0.06 | 0.41 | <1–77 (5) |
W | ppm | <0.1 | <0.1 | <0.1 | <0.1 | <0.1 | <0.1 | <0.1 | <0.1 | <0.1 | nd |
Zn | ppm | 58.4 | 460 | 89 | 89.8 | 132.2 | 50.2 | 39.98 | 34.08 | 48.57 | 4–84 900 (64) |
Sn | ppm | 1.37 | 6.32 | 0.8 | 1.65 | 1.51 | 0.54 | <0.1 | <0.1 | <0.1 | nd |
ecotoxicity levels according to McDonald, Ingersoll (2000) and WT-732 2003 are marked with colors: green – level I, yellow – level II, red – level III.
after Lis and Pasieczna (1998).
Discharges of municipal and industrial wastewater are also a potential source point of cadmium, copper and zinc contamination of the alluvium of the Ner, with the content of these elements higher than the average for the entire Łódź agglomeration in the H and E profiles (Table 4). Significant mercury content reaching a maximum of 0.74 ppm (point H2) was also found in the H and E profiles, and the origin can be seen mainly in the discharge of sewage into the Olechówka and Dobrzynka rivers flowing into the Ner (Lis, Pasieczna 1998).
When analysing the elemental composition of Ner alluvium, one should also pay attention to bismuth. The maximum contents of this element reaching as much as 640 ppm were found in the H profile at point H2. This element was not determined during the research on the Geochemical Atlas of the Łódź agglomeration (Lis, Pasieczna 1998). According to Kabata-Pendias and Pendias (1999), in the zone of hypergenesis, bismuth is not very mobile and is part of insoluble compounds retained by iron hydroxides and manganese and organic matter. Bismuth contents in soils reaching several 100 ppm are found near copper smelters and in metal mining areas (Pasieczna 2012). In the case of the Ner alluvium, such high contents of this element can be associated with pollution supplied to the river with sewage discharged by an unidentified metallurgical plant. In the H2 sample, containing the largest amounts of bismuth, the presence of macroscopically visible fragments of easily crumbling sinters was found. Such a focus on pollution may also be indicated by high values of the coefficient of determination describing the dependence of bismuth content in relation to zinc (
Contamination of alluvial sediments with metals causes their toxic impact on aquatic organisms. According to the criteria used by the Chief Inspectorate for Environmental Protection (GIOŚ), using the values of Threshold Effect Concentration (TEC), Probable Effect Concentration (PEC) and Midpoint Effects Concentrations (MEC) (MacDonald et al. 2000, WT-732 2003), the content in all the samples of arsenic, iron, manganese and nickel allowed them to be included in the first level, i.e. uncontaminated sediments that do not have a negative impact on aquatic organisms. In the case of silver, lead, cadmium, chromium, copper and zinc in some samples, and in the case of mercury in all samples in which this element was determined, second level or third was found, indicating sediment contamination, which may have a negative impact on aquatic organisms. The classification was carried out in terms of elements determined as part of the monitoring of river sediments carried out by the Chief Inspectorate of Environmental Protection (Table 4).
The results of the determination of the CEC of the alluvium accumulated in the Ner river bed, by the Breeuwsma formula and the Kappen method, are similar and indicate a low capacity of these formations to store absorbed substances. This is related to the lithology of river sediments, among which the occurrence of fine-grained sands and sands without a fraction of less than 2 m and with a low content of organic carbon, reaching a maximum of 1.36%, was found (Table 5). The results of the Kappen method indicate that the sorption complex is saturated with acidic cations (e.g. H+, Al3+). The exception is the sample taken at the H2 site, in which the exchange capacity for basic cations (BEC) was two orders of magnitude greater than the electrolytic acidity. It is a sample in which the fragments of easily crumbling sinters were found macroscopically. It is assumed that such a high BEC value in the H2 sample may be the result of dissolution in hydrochloric acid (HCl) of the metals contained in the sediments (e.g. bismuth), and not displacement of basic cations from the sorption complex. It is worth mentioning that due to the lack of the smallest fractions and organic matter, alluvial sediments do not constitute a typical colmation layer here that would retain pollution from the infiltrating river water as known in other studies (Wang et al. 2007).
The cation exchange capacity (CEC) estimated by the Breeuwsma formula and sorption capacity determined by the Kappen method.
Sample no. | TOC content | Particle content below 2 μm | CEC | Hydrolytic acidity | BEC | Total sorption capacity |
---|---|---|---|---|---|---|
[%] | [cmol(+) · kg−1] | [cmol(H+) · kg−1] | [cmol(+) · kg−1] | |||
H1 | 0.69 | 0.00 | 2.40 | 0.6 | 0 | 0.6 |
H2 | 1.30 | 0.00 | 4.56 | 0.68 | 10 | 10.68 |
H3 | 0.23 | 0.00 | 0.81 | 0.45 | 0 | 0.45 |
E1 | 1.36 | 0.00 | 4.76 | 1.73 | 0 | 1.73 |
E2 | 0.72 | 0.00 | 2.52 | 3.23 | 0 | 3.23 |
E3 | 0.61 | 0.00 | 2.13 | 2.03 | 0 | 2.03 |
C1 | 0.60 | 0.00 | 2.10 | 0.6 | 0 | 0.6 |
C2 | 0.19 | 0.00 | 0.66 | 0.45 | 0 | 0.45 |
C3 | 0.31 | 0.00 | 1.09 | 0.83 | 0 | 0.83 |
In terms of the content of macroelements, the Ner water is clearly distinct from both waters taken from river sediments and groundwater (Figs 11 and 12). With their hydrochemical characteristics, the multi-ionic nature of water types (HCO3–Cl–Ca–Na, Cl–HCO3–Na–Ca), with a significant share or even dominance of chloride and sodium ions is noteworthy, which indicates their strong anthropogenic transformation. The poor quality of the water of the Ner River is also represented by the values of electrolytic conductivity exceeding 1200 μS · cm−1, low content of dissolved oxygen (below 4.04 mg · dm−3) and concentrations of nutrients: nitrate nitrogen (over 4.93 mg N-NO3 · dm−3), ammonium nitrogen (above 1.57 mg N-NH4 · dm−3) and phosphate phosphorus (above 0.88 mg P-PO4 · dm−3). The concentrations of the above-mentioned elements in the Ner significantly exceed the threshold values of good chemical status of surface water set out in the Regulation of the Minister of Infrastructure of 25 June 2021 (Journal of Laws 2021, item 1475).
Chemical composition of the tested water presented on the Piper diagram.
Chemistry map of groundwater and river and alluvial waters in the H and E profiles (colors consistent with Fig. 11).
In the alluvium water, among the macroelements, there is a clear dominance of hydrocarbonate and calcium ions. The sulphate, chloride and sodium ions appear as secondary in the water type (Fig. 11, Table 6). The values of the electrolytic conductivity (EC) are lower than those observed in river water and are within a wide range of 469 -1070 μS · cm−1. Similarly, in alluvial water, the average content of nutrients is lower than in river water: 1.71 mg N-NO3 · dm−3, 1.26 mg N-NH4 · dm−3 and 0.29 mg P-PO4 · dm−3. River alluviums are an extremely dynamic zone where surface waters mix with groundwater drained by the river. The shares of individual water streams are constantly changing depending on the temporary pressure systems. Changes in the flow of water result in changes in chemistry. The presented research results describe the temporary hydrochemical state of this zone. It can be assumed that the lower values of EC and the content of nutrients are, apart from the activity of living organisms, caused by the mixing of heavily polluted river water with groundwater in the alluvium, which, according to the conducted research, is of better quality. The EC reached a maximum of 676 μS · cm−1, and the maximum content of nitrate nitrogen 1.36 mg N-NO3 · dm−3, ammonium nitrogen 0.67 mg N-NH4 · dm−3 and phosphate phosphorus 0.03 mg P-PO4 · dm−3.
Physicochemical properties of the tested water.
Parameter | Units | River water | Water from alluvium | Groundwater | Drinking water* | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Hr | Er | H1 | H2 | H3 | C1 | C2 | C3 | E1 | E2 | E3 | Q | Ng | Cr3 | |||
EC | mikroS/cm | 1229 | 1307 | 479 | 469 | 727 | 681 | 737 | 567 | 745 | 875 | 1070 | 649 | 676 | 376 | 2500 |
TDS | mg/ dm3 | 836.6 | 898.9 | 332.7 | 351.17 | 604.7 | 498.5 | 548.9 | 412.3 | 548.8 | 740.9 | 651.2 | 503.3 | 524.7 | 309.8 | |
Water type | HCO3-Cl-Ca-Na | Cl-HCO3-Na-Ca | HCO3-Cl-SO4-Ca | HCO3-Ca | HCO3-SO4-Ca | SO4-HCO3-Ca | HCO3-Ca | HCO3-SO4-Ca | HCO3-Cl-Ca | HCO3-Ca-Na | HCO3-Ca | HCO3-SO4-Ca | HCO3-Ca-Na | HCO3-Ca | ||
pH | 7.3 | 6.46 | 6.5 | 7 | 6.89 | 6.73 | 7.13 | 6.59 | 6.93 | 6.71 | 7.11 | 7.32 | 7.2 | 7.45 | 6.5-9.5 | |
Temp. | st.C | 15.1 | 16.1 | 15.2 | 15.6 | 15.8 | 16.5 | 16.9 | 16.4 | 15.4 | 15.4 | 16.3 | 15.4 | 11.3 | 11.5 | |
Eh | mV | 132 | −28 | −50.1 | −116 | −66.8 | −7.8 | −84 | −58.6 | −63 | −56.5 | −55 | 125 | −53.5 | −66.7 | |
O2 | mg/ dm3 | 3.13 | 4.04 | 1.6 | 0.72 | 1.45 | 1.71 | 1.93 | 1.28 | 1.85 | 1.34 | 1.54 | 1.44 | 0.09 | 0.09 | |
SO42- | mg/ dm3 | 105 | 115 | 55 | 40 | 125 | 155 | 50 | 100 | 75 | 90 | 60 | 100 | 19 | 8 | 250 |
Cl- | mg/ dm3 | 152.93 | 192.85 | 51.69 | 16.59 | 13.83 | 24.96 | 33.25 | 24.74 | 60.97 | 51.33 | 101.39 | 24.04 | 40.63 | 5.25 | 250 |
NO3− | mg/ dm3 | 21.83 | 26.54 | 7.7 | 8.56 | 4.28 | 22.68 | 8.13 | 4.28 | 5.14 | 3.85 | 3.42 | 5.99 | 3.42 | 3.85 | 50 |
NH4+ | mg/ dm3 | 2.02 | 2.24 | 2.07 | 0.97 | 0.45 | 0.15 | 2.6 | 1.83 | 0.5 | 2.2 | 3.84 | 0.01 | 0.86 | 0.36 | 0.5 |
PO43- | mg/ dm3 | 2.9 | 2.75 | 0.08 | 0.48 | 0.1 | 0.12 | 5.6 | 0.52 | 0.33 | 0.06 | 0.88 | 0.08 | 0.06 | 0.08 | |
Al | mg/ dm3 | 0.009 | 0.051 | <0,05 | 0.074 | <0,05 | 0.022 | 0.002 | 0.029 | 0.003 | 0.069 | 0.079 | <0,05 | <0.001 | <0,05 | 0.2 |
As | mg/ dm3 | <0.001 | <0,003 | 0.026 | 0.006 | 0.003 | <0.001 | <0.001 | <0.001 | 0.015 | <0,003 | <0,003 | <0,003 | <0.001 | <0,003 | 0.01 |
Ba | mg/ dm3 | 0.05 | 0.06 | 0.05 | 0.09 | 0.24 | 0.12 | 0.05 | 0.14 | 0.03 | 0.24 | 0.12 | 0.04 | 0.16 | 0.06 | |
Be | mg/ dm3 | nd | <0.005 | <0.005 | <0.005 | <0.005 | nd | nd | nd | nd | <0.005 | <0.005 | <0.005 | nd | <0.005 | |
Bi | mg/ dm3 | <0.005 | 0.09 | <0.005 | 0.1 | 0.07 | <0.005 | <0.005 | <0.005 | <0.005 | <0.005 | 0.04 | 0.06 | <0.005 | <0.005 | |
Pb | mg/ dm3 | <0.001 | 0.003 | 0.002 | 0.006 | 0.002 | <0.001 | <0.001 | <0.001 | 0.013 | 0.003 | 0.004 | 0.002 | <0.001 | 0.002 | 0.01 |
Br | mg/ dm3 | nd | <1 | <1 | <1 | <1 | nd | nd | nd | nd | <1 | <1 | <1 | nd | <1 | |
Cd | mg/dm3 | 0.0080 | 0.0008 | 0.0017 | 0.0028 | 0.0069 | 0.0013 | 0.0009 | 0.0011 | 0.0175 | 0.0016 | 0.0012 | 0.0024 | 0.0005 | 0.0008 | 0.005 |
Ca | mg/ dm3 | 104.57 | 101 | 56.7 | 70.3 | 133 | 102.44 | 99.35 | 83.01 | 95.23 | 123 | 122 | 100 | 75.29 | 62.2 | |
Cr | mg/ dm3 | 0.005 | <0.005 | <0.005 | 0.01 | <0.005 | 0.005 | 0.005 | 0.007 | 0.006 | <0.005 | 0.005 | <0.005 | 0.002 | <0.005 | 0.05 |
Co | mg/ dm3 | <0.005 | <0.005 | <0.005 | <0.005 | <0.005 | <0.005 | <0.005 | <0.005 | <0.005 | <0.005 | <0.005 | <0.005 | <0.005 | <0.005 | |
Fe | mg/ dm3 | 0.04 | 0.36 | 3.34 | 5.26 | 4.17 | 1.39 | 3.19 | 4.54 | 0.1 | 0.75 | 5.14 | <0.02 | 0.67 | 0.64 | 0.2 |
K | mg/ dm3 | 14.43 | 17.6 | 4.75 | 2.48 | 9.34 | 7.16 | 3.94 | 3.39 | 3.76 | 13.1 | 3.07 | 1.32 | 4.16 | 2.52 | |
Cu | mg/ dm3 | 0.001 | <0.005 | <0.005 | 0.005 | <0.005 | <0.001 | <0.001 | <0.001 | <0.001 | <0.005 | <0.005 | <0.005 | <0.001 | <0.005 | 2 |
Mg | mg/ dm3 | 10.64 | 10.5 | 5.3 | 5.43 | 14.3 | 9.18 | 12.76 | 8.83 | 7.9 | 12 | 11.7 | 11.9 | 7.98 | 6.24 | 7-125 |
Mn | mg/ dm3 | 0.113 | 0.122 | 0.361 | 0.51 | 0.296 | 0.32 | 0.384 | 0.542 | 0.002 | 0.257 | 0.749 | 0.088 | 0.042 | 0.036 | 0.05 |
Mo | mg/ dm3 | <0.001 | <0.005 | <0.005 | <0.005 | <0.005 | <0.001 | <0.001 | <0.001 | 0.01 | <0.005 | <0.005 | <0.005 | <0.001 | <0.005 | |
Na | mg/ dm3 | 119.29 | 125 | 16 | 7.76 | 23.2 | 15.23 | 26.2 | 15.62 | 28.76 | 72.9 | 9.52 | 12.1 | 48.37 | 4.94 | 200 |
Ni | mg/ dm3 | 0.009 | 0.014 | 0.006 | <0.005 | <0.005 | 0.006 | 0.001 | 0.005 | 0.007 | 0.006 | <0.005 | <0.005 | <0.001 | <0.005 | 0.02 |
Hg | mg/ dm3 | nd | 0.0017 | 0.0004 | 0.0039 | 0.0004 | nd | nd | nd | nd | 0.0003 | 0.0002 | 0.0013 | nd | 0.0001 | 0.001 |
Ag | mg/ dm3 | nd | <0.005 | <0.005 | <0.005 | <0.005 | nd | nd | nd | nd | <0.005 | <0.005 | <0.005 | nd | <0.005 | 0.01 |
Si | mg/ dm3 | 4.7 | 7.76 | 7.46 | 7.38 | 5.15 | 3.43 | 6.16 | 6.89 | 3.39 | 8.52 | 6.11 | 4.51 | 8.14 | 12.6 | |
Sr | mg/ dm3 | 0.33 | 0.4 | 0.22 | 0.18 | 0.43 | 0.36 | 0.67 | 0.37 | 0.17 | 1.19 | 0.33 | 0.18 | 2.02 | 1.38 | |
Ti | mg/ dm3 | <0.001 | <0.005 | <0.005 | <0.005 | <0.005 | <0.001 | <0.001 | <0.001 | <0.001 | <0.005 | <0.005 | <0.005 | <0.001 | <0.005 | |
V | mg/ dm3 | 0.05 | <0.004 | <0.004 | <0.004 | <0.004 | 0.04 | 0.05 | 0.04 | 0.04 | <0.004 | <0.004 | <0.004 | 0.03 | <0.004 | |
W | mg/ dm3 | <0.001 | <0.005 | <0.005 | <0.005 | <0.005 | <0.001 | <0.001 | <0.001 | 0.02 | <0.005 | <0.005 | <0.005 | <0.001 | <0.005 | |
Zn | mg/ dm3 | 0.06 | 0.09 | 0.06 | 0.06 | 0.06 | 0.08 | 0.05 | 0.03 | 0.02 | 0.05 | 0.06 | 0.09 | <0.001 | 0.02 | |
Sn | mg/ dm3 | <0.001 | <0.005 | <0.005 | <0.005 | <0.005 | <0.001 | <0.001 | <0.001 | <0.001 | <0.005 | <0.005 | <0.005 | <0.001 | <0.005 |
nd – no data, * red numbers in the table mean values exceeding the permissible ranges for drinking water, the ranges are given in accordance with the Regulation of the Minister of Health of December 7, 2017 on the quality of water intended for human consumption (Journal of Laws of 2017, item 2294); the color scale applies to the quality classification of groundwater bodies according to the Regulation of the Minister of Maritime Economy and Inland Navigation of October 11, 2019 on the criteria and method of assessing the status of groundwater bodies: quality class I – dark green, quality class II – light green, III quality class – yellow, quality class IV – orange, quality class V – red.
The collected groundwater samples represent the chemical composition of three aquifers (Fig. 11). The water of the Quaternary is characteris ed by mineralis ation ranging from 100 mg · dm−3 to 1237 mg · dm−3 with the predominance from 100 mg · dm−3 to 400 mg · dm−3 and domination in the composition of hydrocarbonate, calcium and rarely magnesium ion (HCO3–Ca and HCO3–Ca–Mg) (Fabianowski 2002, Rodzoch, Karwacka 2015, Małecki et al. 2017). At the same time, it should be emphasis ed that the higher values of water mineralis ation (above 750 mg · dm−3) were documented during pumping tests within the plateau, with the dominating value of about 500 mg · dm−3 (Murzynowski, Małecki 1982). The physicochemical properties and ionic composition of the groundwater studied today, covering the Quaternary aquifer, are similar to the results of archival research. A general mineralisation of about 500 mg · dm−3 is seen, with a clear dominance of HCO3− and Ca2+ ions (Table 6). However, significant concentrations of sulphate ions (100 mg · dm−3) are noteworthy, exceeding the background range determined by Fabianowski (2002) for this aquifer and allowing the tested water to be classified as HCO3–SO4–Ca.
The Neogene aquifer is exploited only locally due to variable hydrogeological parameters and significant iron and brown coal dust contents (Fabianowski 2002). For this reason, its hydrochemical recognition is insufficient for full characterisation. Based on the research carried out by the authors, it can be concluded that in terms of EC (676 μS · cm−1) and mineralisation (525 mg · dm−3), the tested water is similar to the Quaternary water. Its composition is dominated by hydrocarbonate and calcium ions with a significant share of sodium ions. This is water of the HCO3–Ca–Na type (Table 6).
The Upper Cretaceous aquifer is the most intensively exploited in the area covered by the study. The water of this aquifer is characterised by low electrolytic conductivity ranging from 100 μS · cm−1 to 650 μS · cm−1 and mineralisation of 200–500 mg · dm−3 (Murzynowski, Małecki 1982). These are simple water types of the HCO3–Ca. The collected water sample falls within the background ranges determined for the Upper Cretaceous aquifer: EC = 376 μS · cm−1, TDS = 309.8 mg · dm−3 and water type of HCO3–Ca (Table 6).
It is worth noting that the study by Małecki et al. (2017) and Ziułkiewicz (2003), conducted on the scale of the entire Łódź agglomeration, documented the stability of the chemical composition of the waters of this aquifer during its long-term exploitation. However, on a local scale, a potential inflow of polluted water into the Upper Cretaceous aquifer cannot be omitted, especially in places where hydraulic windows occur between the Quaternary and Cretaceous aquifers.
The impact of anthropopressure on the water chemistry is noticeable not only in their chemical composition, but also in the distribution of speciation of water macroelements. In the case of alkaline elements (Na and K) and alkaline earth metals (e.g. Ca and Mg), the dominance of simple ionic speciation is observed. It is characteristic for water occurring in natural conditions. On the other hand, in surface water, water taken from alluvial water and water of the Quaternary aquifer, the significant share of sulphate and polyelemental speciation is clearly visible, which proves the anthropogenic transformation of their chemistry. In the water from the Upper Cretaceous aquifer, the assessment of sodium and potassium speciation did not reveal the presence of sulphate, and in the case of calcium and magnesium, these speciation are secondary to hydrocarbonate speciation (CaHCO3+ and MgHCO3+) (Table 7). The observed trends in the speciation distribution indicate the high degree of their anthropogenic transformations and are consistent with the results of research conducted by Jóźwiak and Krogulec (2006) in the area of the Warsaw agglomeration.
Percentage contribution of the speciation of selected elements.
Speciation | River water* | Water from alluvium* | Quaternary aquifer (ZP2 well) | Upper Cretaceous (A2 well) | Speciation | River water* | Water from alluvium* | Quaternary aquifer (ZP2 well) | Upper Cretaceous (A2 well) | |
---|---|---|---|---|---|---|---|---|---|---|
Carbon | Magnesium | |||||||||
HCO3− | 71.4 | 70.1 | 87.1 | 89.6 | Mg2+ | 92.9 | 91.5 | 91.8 | 97.0 | |
CO2(aq) | 26.5 | 27.5 | 10.3 | 8.5 | MgSO4 | 4.9 | 5.6 | 5.8 | 0.6 | |
CaHCO3+ | 1.7 | 1.6 | 2.0 | 1.5 | MgHCO3+ | 2.0 | 2.1 | 2.3 | 2.3 | |
MgHCO3+ | 0.2 | 0.2 | 0.3 | 0.2 | MgCl+ | 0.1 | 0.5 | 0.1 | 0.0 | |
NaHCO3 | 0.1 | 0.5 | 0.1 | 0.0 | MgHPO4 | 0.1 | 0.2 | 0.0 | 0.0 | |
CaCO3 | 0.0 | 0.1 | 0.1 | 0.1 | MgCO3 | 0.0 | 0.1 | 0.1 | 0.1 | |
CO32- | 0.0 | 0.0 | 0.1 | 0.1 | Bismuth | |||||
Chlorides | Bi(OH)3(aq) | 94.5 | 93.3 | 98.3 | 98.7 | |||||
Cl- | 99.1 | 99.1 | 99.1 | 99.2 | Bi(OH)2+ | 5.5 | 6.7 | 1.7 | 1.3 | |
CaCl+ | 0.9 | 0.9 | 0.9 | 0.7 | Cadmium | |||||
Sulfur | Cd2+ | 83.1 | 70.2 | 82.5 | 89.6 | |||||
SO42- | 81.1 | 81.8 | 80.7 | 84.8 | CdCl+ | 5.7 | 18.4 | 3.3 | 0.9 | |
CaSO4 | 16.3 | 14.6 | 16.4 | 13.3 | CdSO4(aq) | 5.2 | 4.9 | 6.2 | 0.7 | |
MgSO4 | 2.2 | 2.1 | 2.7 | 1.8 | CdHCO3+ | 4.1 | 3.6 | 4.7 | 4.6 | |
NaSO4− | 0.3 | 1.3 | 0.1 | 0.1 | CdCO3(aq) | 1.1 | 1.4 | 3.1 | 4.1 | |
KSO4− | 0.1 | 0.1 | 0.0 | 0.0 | CdHPO4(aq) | 0.6 | 1.1 | 0.1 | 0.1 | |
NH4SO4− | 0.0 | 0.1 | 0.0 | 0.0 | Cd(SO4)22- | 0.1 | 0.1 | 0.1 | 0.0 | |
Sodium | CdCl2(aq) | 0.0 | 0.3 | 0.0 | 0.0 | |||||
Na+ | 99.4 | 99.3 | 99.3 | 99.5 | CdNO3+ | 0.0 | 0.1 | 0.0 | 0.0 | |
NaHCO3 | 0.4 | 0.4 | 0.5 | 0.5 | Copper | |||||
NaSO4− | 0.2 | 0.3 | 0.3 | 0.0 | Cu2+ | 68.0 | 64.8 | 44.9 | 46.2 | |
Potassium | CuOH+ | 30.7 | 32.1 | 55.0 | 53.5 | |||||
K+ | 99.7 | 99.6 | 99.6 | 100.0 | CuHPO4 | 1.0 | 2.6 | 0.1 | 0.1 | |
KSO4− | 0.3 | 0.4 | 0.4 | 0.0 | CuNH32+ | 0.2 | 0.3 | 0.0 | 0.1 | |
Calcium | CuCl+ | 0.0 | 0.1 | 0.0 | 0.0 | |||||
Ca2+ | 90.6 | 88.3 | 89.3 | 95.5 | Chrome | |||||
CaSO4 | 5.8 | 6.5 | 6.9 | 0.7 | CrO42- | 73.0 | 72.7 | 89.6 | 91.5 | |
CaHCO3+ | 2.9 | 3.0 | 3.3 | 3.4 | HCrO4− | 27.0 | 27.3 | 10.4 | 8.5 | |
CaCl+ | 0.4 | 1.7 | 0.3 | 0.1 | Mercury | |||||
CaCO3 | 0.1 | 0.1 | 0.2 | 0.3 | HgCl2 | 85.5 | 57.3 | 91.4 | 97.9 | |
CaHPO4 | 0.1 | 0.2 | 0.0 | 0.0 | HgCl3− | 14.5 | 42.7 | 8.6 | 2.1 | |
CaNO3+ | 0.1 | 0.2 | 0.0 | 0.0 | Lead | |||||
PbCO3 | 100.0 | 100.0 | 100.0 | 100.0 |
average content.
The characteristics of the content of microelements in water and sediment are also a sensitive indicator of anthropogenic impacts. Studies of the alluvial deposits of the Ner documented the presence of chromium, zinc, copper, mercury and cadmium and, in individual cases, lead and silver in concentrations considered harmful to living organisms. The next step in such an assessment is to determine whether the above-mentioned elements accumulated in river sediments are activated and are also present in water in concentrations that pose a threat to living organisms.
In the tested water samples, the concentration of silver did not exceed the detection limit of 0.005 mg · dm−3 and the limit value for drinking water (0.010 mg · dm−3). The same is true for zinc and copper. The maximum contents of Zn (0.09 mg · dm−3) and Cu (0.005 mg · dm−3) do not exceed the contents that may have a negative impact on living organisms. In the case of copper, they also do not exceed the limit values for drinking water (Table 6).
Concentrations of chromium are considered in surface water as harmful to biological activity with content exceeding 0.1 mg · dm−3 (Kabata-Pendias, Pendias 1999), and in drinking water, the content of this element should not exceed 0.05 mg · dm−3 (Journal of Laws of 2017, item 2294). In the tested water samples, the chromium content was lower than the limit values given above. The highest concentrations, reaching 0.010 mg · dm−3, were found in the water taken from the alluvium of the Ner River. The results of speciation modelling indicate that this element occurs mainly in the sixth oxidation state in the form of the easily soluble CrO42- form (Tables 6 and 7). This is worrying because forms of hexavalent chromium are mobile in the soil and water environment and are subject to intensive bioaccumulation (Kabata-Pendias, Pendias 1999).
The contents of cadmium, mercury, arsenic and lead in water from the alluvium of Ner, in individual samples, exceed the limit values for drinking water, which are: 0.005 mg Cd · dm−3, 0.01 mg Pb · dm−3, 0.01 As · dm−3 and 0.001 mg Hg · dm−3 (Journal of Laws of 2017, item 2294). In addition, mercury concentrations exceed the values allowed for drinking water also in the sample taken from the Quaternary aquifer (0.00132 mg · dm−3). It should be emphasised that all forms of mercury are toxic. Mercury easily passes from adsorbed forms to water (Kabata-Pendias, Pendias 1999). Extreme mercury content in the water taken from the Ner alluvium significantly exceeds the Hg content found both in the analysed groundwater and surface water, which may indicate the release of mercury accumulated in the alluvium into the solution. The same trend was observed for cadmium, lead and bismuth, and for zinc, the course of the cumulative curve for surface water and alluvial water is similar, lower values occur in groundwater (Figs 12 and 13).
Cumulative concentration curves of selected microelements in water (n = 14).
The analysis of microelements concentrations in the tested waters in the case of their mixing indicates a negative impact of water from alluvial sediments on the chemical status of waters of the Quaternary and Upper Cretaceous horizons.
The assessment of hydraulic relationships between surface water and groundwater, and the relationships between aquifers are fundamental elements determining the sensitivity of the hydrogeological system to pollution in river valley zones exposed to strong anthropopressure. The disturbance of the hydrodynamic balance of the Upper Cretaceous aquifer showed that despite the existence of significant pressure values in the Cretaceous (H well 0.4 atm., C well 0.15 atm.), there are zones (E well) where the pressure in the Upper Cretaceous horizon decreased as a result of groundwater withdrawal. This will lead to the drainage of water from the above aquifers and pose a threat to the chemical status of the water in the Cretaceous aquifer.
To assess this threat, a numerical model of the groundwater system in the Konstantynów Łódzki region was created, taking into account groundwater withdrawal from the Upper Cretaceous aquifer in Ignacew, located near the Ner river valley. Model tests have shown that when group pumping of the A1, A2 and A3 Ignacew wells with actual discharge rate occurs, the water inflow to all wells takes place through the Ner river valley in the area of the research profiles and hydrogeological cross-sections of C and E, where the occurrence of hydrogeological windows between the Quaternary and Cretaceous aquifers was found.
Hydrochemical characteristics of surface water and groundwater in this region showed that in terms of macroelements content, the waters of the Ner river are clearly different from both water collected from river sediments and groundwater (Fig. 11). River waters are characterised by polyionic types (HCO3–Cl–Ca–Na, Cl–HCO3–Na–Ca) with a significant share or even dominance of chloride and sodium ions, which indicates their strong anthropogenic transformation. The waters of the Quaternary aquifer are characterised by mineralisation ranging from 100 mg · dm−3 to 1237 mg · dm−3 with the predominance of waters ranging from 100 mg · dm−3 to 400 mg · dm−3 and the dominance of the following composition: bicarbonates, calcium ions, and locally magnesium ions (water type of HCO3–Ca and HCO3–Ca–Mg).
Higher values of water mineralisation (above 750 mg · dm−3) were documented during test pumping in the plateau, and lower values in the Ner river valley, with an average value of approximately 500 mg · dm−3. The groundwater of the Quaternary aquifer is water with a total mineralisation of approximately 500 mg · dm−3, with a clear dominance of HCO3− and Ca2+ ions and significant contents of sulphate ions (100 mg · dm−3), exceeding the background range of the Quaternary aquifer, classifying tested waters to the type HCO3–SO4–Ca. The Neogene aquifer was characterised by variable hydrochemical parameters and significant contents of iron and lignite dust. The Upper Cretaceous aquifer, which is most intensively exploited in the study area, is characterised by low electrolytic conductivity ranging from 100 μS · cm−1 to 650 μS · cm−1 and mineralisation of 200–500 mg · dm−3. These are waters of the HCO3–Ca type. The results of archival and contemporary research indicate the stability of their chemical composition during long-term exploitation.
Anthropogenic changes in water chemistry are noticeable not only in their composition, but also in the share of macroelement speciations. In surface water, water taken from alluvium and water of the Quaternary aquifer, there is a clearly higher share of sulphate forms and multi-element speciation, indicating the anthropogenic transformation of their chemistry. However, in the water of the Upper Cretaceous aquifer, the dominance of simple ionic forms is observed, characteristic of water occurring in natural conditions. Water pollution in the near-surface zone is also documented by the concentration of cadmium, mercury and lead. In the water from the Ner alluvium, in individual samples, they exceed the permissible values for drinking water. Also in a sample taken from the Quaternary aquifer, mercury concentrations exceed the permissible values for drinking water. High mercury content in water collected from the Ner alluvium, significantly exceeded the Hg content found in the analysed groundwater and surface water, indicating the release of mercury accumulated in the alluvium from adsorbed forms to the solution. A similar tendency was observed in the case of cadmium and lead.
The results of the research showed that the accumulated pollutant loads in the near-surface zones of the studied area actually pose a threat to the Upper Cretaceous aquifer. Maintaining good chemical condition of this aquifer is conditional on strict compliance with the current withdrawal. Limiting exploitation by monitoring discharge rates will allow maintaining the current pressure gradients, which will minimise the possibility of releasing accumulated pollutants. These findings should be used in the management of groundwater in the studied region, in documenting groundwater withdrawal in planning and in water-protection issues. At the same time, in the active and monitoring wells located on the plateau and in the Ner valley, monitoring of the chemical state of Quaternary and Upper Cretaceous water should be carried out in accordance with the schedule specified in the Regulation of the Minister of Infrastructure of 13th July 2021, on the forms and methods of monitoring surface water and groundwater bodies (Journal of Laws of 2021, item 1576) every 6 years.
In the regional assessment, in connection with the designation of the protection areas of the Main Groundwater Reservoirs for the purposes of planning and managing water in river basin areas, it is necessary to indicate places of groundwater quality threat, especially of the useful aquifers. Undoubtedly, such threats occur in river valley zones, which for decades have been the site of sewage discharge from large urban agglomerations, an example of which is the Ner river valley.